For histogram diff, we can afford a smaller sample size and thus a
poorer estimate of the number of lines, as the hash table (rhash) won't
be filled up/grown. This is safe as the final count of lines (xdf.nrecs)
will be updated correctly anyway by xdl_prepare_ctx().
This gives us a small boost in performance.
Signed-off-by: Tay Ray Chuan <rctay89@xxxxxxxxx>
---
xdiff/xprepare.c | 17 ++++++++++++++---
xdiff/xutils.c | 8 ++------
xdiff/xutils.h | 2 +-
3 files changed, 17 insertions(+), 10 deletions(-)
diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
index 7556538..dfbb0de 100644
--- a/xdiff/xprepare.c
+++ b/xdiff/xprepare.c
@@ -26,6 +26,8 @@
#define XDL_KPDIS_RUN 4
#define XDL_MAX_EQLIMIT 1024
#define XDL_SIMSCAN_WINDOW 100
+#define XDL_GUESS_NLINES1 256
+#define XDL_GUESS_NLINES2 20
typedef struct s_xdlclass {
@@ -239,11 +241,20 @@ static void xdl_free_ctx(xdfile_t *xdf) {
int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
xdfenv_t *xe) {
- long enl1, enl2;
+ long enl1, enl2, sample;
xdlclassifier_t cf;
- enl1 = xdl_guess_lines(mf1) + 1;
- enl2 = xdl_guess_lines(mf2) + 1;
+ /*
+ * For histogram diff, we can afford a smaller sample size and
+ * thus a poorer estimate of the number of lines, as the hash
+ * table (rhash) won't be filled up/grown. The number of lines
+ * (nrecs) will be updated correctly anyway by
+ * xdl_prepare_ctx().
+ */
+ sample = xpp->flags & XDF_HISTOGRAM_DIFF ? XDL_GUESS_NLINES2 : XDL_GUESS_NLINES1;
+
+ enl1 = xdl_guess_lines(mf1, sample) + 1;
+ enl2 = xdl_guess_lines(mf2, sample) + 1;
if (!(xpp->flags & XDF_HISTOGRAM_DIFF) &&
xdl_init_classifier(&cf, enl1 + enl2 + 1, xpp->flags) < 0) {
diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index ded7c32..a45e89b 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -24,10 +24,6 @@
-#define XDL_GUESS_NLINES 256
-
-
-
long xdl_bogosqrt(long n) {
long i;
@@ -159,12 +155,12 @@ void *xdl_cha_next(chastore_t *cha) {
}
-long xdl_guess_lines(mmfile_t *mf) {
+long xdl_guess_lines(mmfile_t *mf, long sample) {
long nl = 0, size, tsize = 0;
char const *data, *cur, *top;
if ((cur = data = xdl_mmfile_first(mf, &size)) != NULL) {
- for (top = data + size; nl < XDL_GUESS_NLINES;) {
+ for (top = data + size; nl < sample;) {
if (cur >= top) {
tsize += (long) (cur - data);
if (!(cur = data = xdl_mmfile_next(mf, &size)))
diff --git a/xdiff/xutils.h b/xdiff/xutils.h
index 674a657..714719a 100644
--- a/xdiff/xutils.h
+++ b/xdiff/xutils.h
@@ -33,7 +33,7 @@ void xdl_cha_free(chastore_t *cha);
void *xdl_cha_alloc(chastore_t *cha);
void *xdl_cha_first(chastore_t *cha);
void *xdl_cha_next(chastore_t *cha);
-long xdl_guess_lines(mmfile_t *mf);
+long xdl_guess_lines(mmfile_t *mf, long sample);
int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags);
unsigned long xdl_hash_record(char const **data, char const *top, long flags);
unsigned int xdl_hashbits(unsigned int size);
--
1.7.3.4.681.gb718e
--
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